Elevator systems include a car situated in a hoistway for carrying passengers between various floors in a building, for example. A motor provides the force needed to move the elevator car. A drive causes desired operation of the motor to achieve desired elevator car movement.
An elevator system drive can be considered to have a power section and a control section. The power section, which typically includes components such as IGBTs or other switches, is sometimes electrically referenced to a DC bus. The control section, on the other hand, is electrically referenced to ground.
One issue presented by referencing the power section of a drive to the DC bus is that the DC bus is not referenced to ground. This is particularly true in regenerative drives. In that case, the DC bus potential moves significantly relative to ground with the switching of the input converter power devices. As a result, isolation is required for all control signals to the power section and all feedback signals from the power section. Example feedback signals include input and output converter current sensing, input and output converter IGBT gate commands and DC bus voltage sensing.
The isolation required between the differently electrically referenced portions of the drive introduces complexity and cost. The costs associated with isolating the control components from the power components can be a significant portion of some elevator drives.